Surface-treated steel plate for battery case and battery case

ABSTRACT

A battery case excellent in glossiness of appearance and working efficiency and a surface-plated steel plate which can be used preferably to manufacture the battery case. The battery case is produced by deep-drawing, DI-forming, DTR-forming a surface-treated steel plate having glossy nickel or glossy nickel-cobalt alloy plating on the outermost layer corresponding to the external face of a battery case of a plated original plate consisting of a steel plate. The glossy nickel plating or glossy nickel-cobalt alloy plating layer on the outermost layer has a high glossiness, and therefore the appearance is excellent. The runnability of a formed battery case is high as well as the working efficiency.

RELATED APPLICATIONS

The present application is a continuation of parent application Ser. No.10/343,765, nationalized Feb. 4, 2003, which was the U.S. national stageof international application PCT/JP 01/05245, filed Jun. 20, 2001.

TECHNICAL FIELD

The present invention relates to a container, in which an alkali liquidis enclosed, and more specifically, it relates to a surface-treatedsteel plate for an exterior case of a battery, such as an alkalinemanganese battery, a nickel-cadmium battery and the like, and a batterycase obtained by subjecting the surface-treated steel plate to adeep-drawing method, a DI-forming method or a DTR-forming method.

BACKGROUND ART

For a battery case enclosing a strong alkaline liquid for an alkalinemanganese battery, a nickel-cadmium battery and the like, a method suchthat a cold-rolled steel strip is press-formed into a battery case andthen subjected to barrel plating or a method such that a nickel platedsteel strip is press-formed into a battery case have conventionally beenemployed.

In this way, for the use of battery, such as an alkaline manganesebattery, a nickel cadmium battery and the like, nickel plating is usedbecause nickel is strong for alkaline corrosiveness and these batteriesmainly utilize strong alkali potassium hydroxide as electrolyte.Further, in the case battery is connected to an external terminal,nickel has stable contact resistance. Furthermore, there is an advantagein the manufacture of battery that nickel has excellent spotweldability, in which spot welding is carried out to weld eachconstituent parts to be assembled in a battery.

In order to increase battery capacity in recent years, a DI (drawing andironing) forming method is used instead of a deep-drawing method(JP-B-7-99686) as a press-formed method for a battery case. In theDI-forming method and a DTR (drawing thin and redraw) method, anode andcathode active substances can be enclosed in a larger amountcorresponding to a smaller thickness of the side wall of the case thanthe thickness of the bottom, and an advantage can also be obtained suchthat the pressure strength of the battery can be improved owing to thethick bottom of the case along with an increase of battery capacity.

Furthermore, the demand of an alkaline manganese battery and a nickelhydoride battery has increased in recent years, and automization ofproduction of batteries is progressing accordingly. Owing thereto, abattery case having been press-formed is automatically conveyed to abattery case washing machine and a battery producing machine with a beltconveyor. However, in the case where the outer surface of the batteryhas poor slipping property, the battery case is stopped on the way in onthe belt conveyor to delay supply of the battery case to the batterywashing machine or the battery production process, whereby the workingefficiency is deteriorated.

In recent years, with respect to battery cases produced by thedeep-drawing method, the DI-forming method and the DTR-forming method, alarge amount of the battery cases are placed on a belt conveyor and runby for producing batteries. However, they do not run smoothly with aconventional nickel plating on the outermost layer of the outer surfaceof the battery case, whereby the supply of the battery cases is liableto be intermittent. In particular, upon entering the battery casesrunning on the belt conveyor into a process step of arranging them intolines, clogging is liable to occur with the nickel on the outermostlayer of the outer surface of the battery case.

A technical object of the invention is to provide a battery case that isexcellent in glossiness and runnability, and a surface-treated steelplate that can be preferably used for producing the battery case.

DISCLOSURE OF THE INVENTION

In this connection, the inventors have found from the foregoingstandpoint that in the case where a battery case produced by thedeep-drawing method, the DI-forming method and the DTR-forming methodhas glossy nickel plating or glossy nickel-cobalt alloy layer on theoutermost layer of the outer surface of the canister, the flowingproperty of the battery case on a belt conveyor is excellent. It isexpected that the runnability of a battery case is good when the outersurface of the case is hard and has a small friction coefficient.Furthermore, it has been found that the addition of cobalt improves theglossiness of the plated surface.

In order to attain the object, a surface-treated steel plate for abattery case of claim 1 is characterized by having an iron-nickeldiffusion layer as a lower layer and a nickel layer as an upper layer ona surface corresponding to an inner surface of the case, and aniron-nickel diffusion layer as a lower layer, a nickel layer as anintermediate layer and a glossy nickel plating layer as an upper layeron a surface corresponding to an outer surface of the case.

A surface-treated steel plate for a battery case of claim 2 ischaracterized by having an iron-nickel diffusion layer on a surfacecorresponding to an inner surface of the case, and an iron-nickeldiffusion layer as a lower layer, a nickel layer as an intermediatelayer and a glossy nickel plating layer as an upper layer on a surfacecorresponding to an outer surface of the case.

A surface-treated steel plate for a battery case of claim 3 ischaracterized by having an iron-nickel diffusion layer as a lower layer,a nickel layer as an intermediate layer and a nickel plating layer as anupper layer on a surface corresponding to an inner surface of the case,and an iron-nickel diffusion layer as a lower layer, a nickel layer asan intermediate layer and a glossy nickel plating layer as an upperlayer on a surface corresponding to an outer surface of the case.

A surface-treated steel plate for a battery case of claim 4 ischaracterized by having an iron-nickel diffusion layer as a lower layerand a nickel plating layer as an upper layer on a surface correspondingto an inner surface of the case, and an iron-nickel diffusion layer as alower layer, a nickel layer as an intermediate layer and a glossy nickelplating layer as an upper layer on a surface corresponding to an outersurface of the case.

A surface-treated steel plate for a battery case of claim 5 ischaracterized by having an iron-nickel diffusion layer as a lower layerand a nickel layer as an upper layer on a surface corresponding to aninner surface of the case, and an iron-nickel diffusion layer as a lowerlayer, a nickel layer as an intermediate layer and a glossy nickel alloyplating layer as an upper layer on a surface corresponding to an outersurface of the case.

A surface-treated steel plate for a battery case of claim 6 ischaracterized by having an iron-nickel diffusion layer on a surfacecorresponding to an inner surface of the case, and an iron-nickeldiffusion layer as a lower layer, a nickel layer as an intermediatelayer and a glossy nickel alloy plating layer as an upper (layer on asurface corresponding to an outer surface of the case.

A surface-treated steel plate for a battery case of claim 7 ischaracterized by having an iron-nickel diffusion layer as a lower layer,a nickel layer as an intermediate layer and a nickel plating layer as anupper layer on a surface corresponding to an inner surface of the case,and an iron-nickel diffusion layer as a lower layer, a nickel layer asan intermediate layer and a glossy nickel alloy plating layer as anupper layer on a surface corresponding to an outer surface of the case.

A surface-treated steel plate for a battery case of claim 8 ischaracterized by having an iron-nickel diffusion layer as a lower layerand a nickel plating layer as an upper layer on a surface correspondingto an inner surface of the case, and an iron-nickel diffusion layer as alower layer, a nickel layer as an intermediate layer and a glossy nickelalloy plating layer as an upper layer on a surface corresponding to anouter surface of the case.

The nickel plating layer may either be non-glossy nickel plating,semi-glossy nickel plating or glossy nickel plating. The glossy nickelalloy plating layer may be glossy nickel-cobalt plating. It is preferredthat the thickness of the nickel layer is from 0.01 to 3 μm. It ispreferred that the thickness of the nickel plating layer is from 0.2 to3 μm. It is preferred that the thickness of the glossy nickel platinglayer or the glossy nickel alloy plating layer is from 0.5 to 4 μm.

A battery case of claim 15 is a battery case characterized by beingformed by subjecting a surface-treated steel plate for a battery casedescribed in claims 1 to 14 to a deep-drawing method, a DI-formingmethod or a DTR-forming method.

BEST MODE FOR CARRYING OUT THE INVENTION

With respect to the formation of the glossy nickel-cobalt alloy platingin the battery case and the surface-treated steel plate described in theforegoing, in the case where cobalt sulfate is added to a Watts bath ora sulfamic acid bath, cobalt is eutected with nickel, and as a result,an eutectoid plating layer increases in glossiness and increases inhardness of the plating film layer along with increase of the cobaltcontent in the plating film. Specifically, The plating glossiness ofglossy nickel plating with a sulfuric acid bath is from 460 to 470(according to the mirror surface glossiness measuring method, JIS Z8741)in the case of no cobalt added, whereas it increases to from 507 to 525(according to the mirror surface glossiness measuring method, JIS Z8741)with a cobalt content of 1.0%, for example. Glossy nickel plating withno cobalt added also exerts the effect.

The invention can provide improvement of the runnability of canistersirrespective to the formation method of the battery case, for example,irrespective to a deep-drawing method, a DI-forming method or aDTR-forming method, and thus can be preferably used.

The cobalt content of the glossy nickel-cobalt alloy plating ispreferably in a range of from 0.5 to 10%. When the cobalt content isless than 0.5%, there is no effect on improvement in glossiness or onrunnability of canisters owing to the addition of cobalt, whereas in thecase where the cobalt content exceeds 10%, the effect on runnability ofcanisters is saturated, and it is uneconomical as cobalt is an expensivenoble metal. Glossy nickel plating added with a gloss agent, to which nocobalt is added, also exerts the effect.

The plating thickness of the surface-treated steel plate in the case ofthe glossy nickel plating or the glossy nickel-cobalt alloy plating ofthe invention is preferably in a range of from 0.5 to 4 μm on a sidecorresponding to an outer surface of the case.

When the thickness of the glossy nickel plating or the glossynickel-cobalt alloy plating on the side of the outer surface of the caseis less than 0.5 μm, there is no effect on improvement in glossiness orrunnability of the battery case. When the plating thickness exceeds 4.0μm, the effect of improvement in runnability of the battery case reachessaturation, and further thickening is uneconomical.

As a steel plate as a mother material for the surface-treated steelplate, i.e., a plated original plate, in general, a low-carbon aluminumkilled steel is preferably used. Furthermore, a cold-rolled steel stripproduced from a nonageing ultra-low carbon steel (less than 0.01% ofcarbon) with niobium and titanium added is also used.

The steel strip is then subjected, after cold-rolling, to electrolyticcleaning, annealing and tempering rolling in ordinary manners to make aplated original plate. Thereafter, nickel plating is made on bothsurface of the plated original plate. After the plating, a nickel-irondiffusion layer is formed by a thermal treatment. The thermal treatmentis carried out under such conditions that a nickel-iron alloy layer isformed as the entire amount, or a nickel layer remains by 3 μm or lessin thickness. For the object, a temperature of from 450 to 650° C. and atime of from 4 to 15 hours are preferred for a thermal treatment by abox type annealing method, and a temperature of from 600 to 850° C. anda time of from 0.5 to 3 minutes are preferred for a thermal treatment bya continuous annealing method.

Thereafter, glossy nickel plating or glossy nickel alloy plating isapplied on a surface corresponding to an outer surface of a batterycase. The glossy nickel alloy plating is preferably nickel-cobalt alloyplating.

As another method, after carrying out glossy nickel plating or glossynickel alloy plating on a surface corresponding to an outer surface of abattery case as same as described in the foregoing, non-glossy nickelplating, semi-glossy nickel plating or glossy nickel plating is made ona surface corresponding to an inner surface. In the case where glossynickel plating is carried out, it can be simultaneously carried out withthe glossy nickel plating on the side of the outer surface. The platingthickness is preferably in a range of from 0.2 to 3 μm. When it is lessthan 0.2 μm, no effect is observed on improvement in batteryperformance, whereas when it exceeds 3 μm, the effect is saturated, andcost rise is brought about with an unnecessarily large thickness.

While the plating bath may be a known sulfate bath or sulfonamide bath,a sulfate bath is preferred as bath handling thereof is relativelyconvenient. Because the deposition ratio of cobalt and nickel in theplating film is higher by several times than the concentration ratio inthe plating bath, it is possible that a nickel anode is used as ananode, and supply of cobalt ion is carried out by addition in the formof a sulfamate or a sulfate.

EXAMPLES

The invention will be further described in detail with reference to thefollowing examples.

Low-carbon aluminum killed steel plates having a thickness of 0.25 mmand 0.4 mm having been subjected to cold rolling, annealing and temperrolling were used as a plated original plate, respectively. Ultra-lowcarbon aluminum killed steel plates having a thickness of 0.25 mm and0.4 mm having been subjected to cold rolling were used as platedoriginal plates. The steel chemical composition of both the platedoriginal plates was as follows.

-   -   C: 0.04%        (percentage in terms of % by weight, hereinafter the same)    -   Si: 0.01%    -   Mn: 0.22%    -   P: 0.012%    -   S: 0.006%    -   Al: 0.048%    -   N: 0.0025%

The plated original plates were subjected to pretreatment includingalkaline electrolytic degreasing, water washing, dipping in a solutioncontaining a sulfuric acid and water washing in ordinary manners, andthen subjected to ordinary non-glossy nickel plating.

(1) Non-Glossy Nickel Plating

Non-glossy nickel plating was carried out by using the following nickelsulfate bath.

Bath composition Nickel sulfate NiSO₄.6H₂O 300 g/L Nickel chlorideNiCl₂.6H₂O  45 g/L Boric acid H₃BO₃  30 g/L Bath pH: 4 (adjusted withsulfuric acid) Stirring: Air stirring Bath temperature: 60° C. Anode: SPellet (a trade name, produced by INCO Inc., spherical) charged in atitanium basket and covered with a polypropylene bag was used.

After the non-glossy nickel plating, a nickel-iron diffusion layer isformed by a thermal treatment. The thermal treatment was carried outunder conditions of a non-oxidizing atmosphere of 6.5% of hydrogen withthe balance of nitrogen gas and a dew point of −55° C. to make a nickellayer of from 0.01 to 3 μm remaining as the outermost layer or anickel-iron alloy layer formed as the entire amount by appropriatelychanging the soaking time and the soaking temperature.

Furthermore, glossy nickel plating or glossy nickel-cobalt alloy platingwas carried out on a surface corresponding to the outer surface of thebattery case. The glossy nickel plating was carried out with thefollowing glossy nickel-cobalt alloy plating bath, to which cobaltsulfate was not added.

(2) Glossy Nickel-Cobalt Alloy Plating

Cobalt sulfate was appropriately added to a nickel sulfate bath to makecobalt contained in a nickel plating layer. Bath Composition Nickelsulfate NiSO₄.6H₂O 300 g/L Nickel chloride NiCl₂.6H₂O  45 g/L Cobaltsulfate CoSO₄.6H₂O (adlibitum) Boric acid H₃BO₃  30 g/LNitrogen-containing heterocyclic compound  0.6 g/L Nitrogen-containingaliphatic compound  2.0 g/L Bath pH: 4 (adjusted with sulfuric acid)Stirring: Air stirring Bath temperature: 60° C.Anode: S Pellet (a trade name, produced by INCO Inc., spherical) chargedin a titanium basket and covered with a polypropylene bag was used.Under the foregoing conditions, the cobalt content and the platingthickness of the plating film were changed by changing the additionamount of cobalt sulfate and the electrolysis time. While goodcharacteristics were obtained until the forgoing surface treatment,non-glossy nickel plating, semi-glossy nickel plating or glossy nickelplating may further be carried out on the inner surface of the batterycase. The plating bath described in the foregoing can be used as aplating bath for non-glossy nickel plating. In the case of the glossynickel plating, it may be carried out simultaneously with glossy nickelplating carried out on the outer surface of the battery case.

The following plating bath is used for semi-glossy nickel plating. Thesemi-glossy nickel plating may be carried out instead of the initialnon-glossy nickel plating.

(3) Semi-Glossy Nickel Plating

Semi-glossy nickel plating was carried out by appropriately adding apolyoxyethylene adduct of an unsaturated alcohol and an unsaturatedcarboxylic acid formaldehyde as a semi-glossy agent. Bath compositionNickel sulfate NiSO4.6H2O 300 g/L Nickel chloride NiCl2.6H2O  45 g/LBoric acid H3BO3  30 g/L Polyoxyethylene adduct of unsaturated alcohol 3.0 g/L Unsaturated carboxylic acid formaldehyde  3.0 g/L Bath pH: 4(adjusted with sulfuric acid) Stirring: Air stirring Bath temperature:60° C.Anode: S Pellet (a trade name, produced by INCO Inc., spherical) chargedin a titanium basket and covered with a polypropylene bag was used.(Production of Battery Case)

Production of a battery case by the DI-forming method was carried out insuch a manner that the plated steel plate having a thickness of 0.4 mmwas subjected to cupping from a blank diameter of 41 mm to a diameter of20.5 mm, and then subjected to redrawing and two-step ironing formingwith a DI-forming machine to be formed into an outer diameter of 13.8mm, a case wall of 0.20 mm and a height of 56 mm. An upper part wasfinally trimmed to produce an LR6 type battery case having a height of49.3 mm.

Production of a battery case by the DTR-forming method was carried outin such a manner that the plated steel plate having a thickness of 0.25mm was punched to a blank diameter 58 mm and subjected to several timesof drawing and redrawing to produce an LR6 type battery case having anouter diameter of 13.8 mm, a case wall of 0.20 mm and a height of 49.3mm.

Furthermore, production of a battery case by the deep-drawing method wascarried out in such a manner that the plated steel plate having athickness of 0.25 mm was punched to a blank diameter 57 mm and subjectedto several times of drawing and redrawing to produce an LR6 type batterycase having an outer diameter of 13.8 mm, a case wall of 0.25 mm and aheight of 49.3 mm. TABLE 1 Ni Inner Soaking thickness Battery FlowingExample or surface Ni plating conditions on outer- Plating canisterproperty Comparative Thickness or outer thickness on thermal most layerKind of Thickness production of battery Discharging Example (mm) surface(μm) treatment (μm) plating (μm) method case Characteristics Example 10.40 inner 3.0 500° C. × 5 hours 1.0 — — DI ◯ ◯ surface forming outer3.0 1.0 glossy Ni- 1.0 surface 3% Co Example 2 0.25 inner 2.5 450° C. ×15 hours 1.0 — — DTR ◯ ◯ surface forming outer 4.0 2.0 glossy Ni- 0.5surface 10% Co Example 3 0.40 inner 1.0 650° C. × 4 hours 0.0 — — DI ◯ ◯surface forming outer 2.0 1.0 glossy Ni- 3.0 surface 0.5% Co Example 40.25 inner 1.5 600° C. × 3 minutues 1.0 — — deep- ◯ ◯ surface drawingouter 4.0 2.0 glossy Ni 0.5 forming surface Example 5 0.40 inner 4.0850° C. × 0.5 minutes 2.0 — — DI ◯ ◯ surface forming outer 4.0 2.0glossy Ni 3.0 surface Example 6 0.40 inner 0.2 500° C. × 5 hours 0.0non-glossy 1.0 DI ◯ ◯ surface Ni forming outer 4.0 1.2 glossy Ni- 2.0surface 0.5% Co Example 7 0.25 inner 2.5 450° C. × 15 hours 1.5semi-glossy 0.2 DTR ◯ ◯ surface Ni forming outer 2.5 1.5 glossy Ni- 0.5surface 10% Co Example 8 0.40 inner 3.0 650° C. × 4 hours 1.0 glossy Ni0.5 DI ◯ ◯ surface forming outer 3.5 1.0 glossy Ni- 3.0 surface 2% CoExample 9 0.25 inner 0.5 600° C. × 3 minutes 0.0 non-glossy 2.0 deep- ◯◯ surface Ni drawing outer 1.5 1.0 glossy Ni 0.5 forming surface Example10 0.40 inner 4.0 850° C. × 0.5 minutes 1.5 semi-glossy 1.0 DI ◯ ◯surface Ni forming outer 4.0 1.5 glossy Ni 4.0 surface Comparative 0.40inner 3.0 500° C. × 5 hours 1.0 — — DI (reference) (reference) Example 1surface forming outer 3.0 1.0 — — surface(Runnability of Battery Case)

The runnability of a battery case was measured in such a manner that 100of battery cases were placed on a belt conveyor, and the width wasnarrowed to pass only one of the battery cases where they had beenconveyed with the belt conveyor. The case where the time for passing 100battery cases was shorter than Comparative Example 1 was evaluated as“◯”. The results are shown in Table 1.

(Charging Characteristics of Battery)

An AA size alkaline manganese battery was produced by using the batterycase. The battery thus produced was discharged through a load resistanceof 2 Ω, and a discharging time until a voltage of 0.9 V was measured. Asa result, the case where the discharging time was equal to or longerthan Comparative Example 1 was evaluated as “Ω”. The results are shownin Table 1.

APPLICABILITY IN INDUSTRY

A battery case having glossy nickel plating or glossy nickel-cobaltalloy plating on the outermost layer on the outer surface obtained by adeep-drawing method, a DI-forming method or a DTR-forming method is goodin runnability of the battery case, and operations of battery productioncan be smoothly carried out. The battery performance (dischargingcharacteristics) is also good.

1. A surface-treated steel plate for a battery case having a firstiron-nickel diffusion layer on a surface corresponding to an innersurface of the case, and a second iron-nickel diffusion layer on anopposite surface of said steel plate, a nickel layer as an intermediatelayer over said second iron-nickel layer, and a glossy nickel platinglayer as an upper layer on a surface corresponding to an outer surfaceof the case over said intermediate nickel layer.
 2. A surface-treatedsteel plate for a battery case having a first iron-nickel diffusionlayer as a lower layer, a first nickel layer as an intermediate layerover said first iron-nickel diffusion layer, and a nickel plating layeras an upper layer on a surface corresponding to an inner surface of thecase over said first nickel layer, and a second iron-nickel diffusionlayer as a lower layer, a second nickel layer as an intermediate layerover said second iron-nickel diffusion layer, and a glossy nickelplating layer as an upper layer on a surface corresponding to an outersurface of the case over said second nickel layer.
 3. A surface-treatedsteel plate for a battery case having a first iron-nickel diffusionlayer as a lower layer and a first nickel plating layer as an upperlayer on a surface corresponding to an inner surface of the case oversaid first iron-nickel diffusion layer, and a second iron-nickeldiffusion layer as a lower layer, a second nickel layer as anintermediate layer over said second iron-nickel diffusion layer, and aglossy nickel plating layer as an upper layer on a surface correspondingto an outer surface of the case over said second nickel layer.
 4. Asurface-treated steel plate for a battery case having a firstiron-nickel diffusion layer on a surface corresponding to an innersurface of the case, and a second iron-nickel diffusion layer as a lowerlayer, a nickel layer as an intermediate layer over said second nickeldiffusion layer, and a glossy nickel alloy plating layer as an upperlayer on a surface corresponding to an outer surface of the case oversaid nickel layer.
 5. The surface-treated steel plate for a battery caseof claim 3 or 4, wherein the nickel plating layer is either non-glossynickel plating, a semi-glossy nickel plating or a glossy nickel plating.6. The surface-treated steel plate for a battery case of claim 4,wherein the glossy nickel alloy plating layer is glossy nickel-cobaltplating.
 7. The surface-treated steel plate for a battery case of claims1-4, wherein the nickel layer has a thickness from 0.01 to 3 μm.
 8. Thesurface-treated steel plate for a battery case of claims 2 or 3, whereinthe nickel plating layer has a thickness from 0.2 to 3 μm.
 9. Thesurface-treated steel plate for a battery case of claims 1-4, whereinthe glossy nickel plating layer has a thickness from 0.5 to 4 μm. 10.The surface-treated steel plate for a battery case of claim 4, whereinthe glossy nickel alloy plating layer has a thickness of from 0.5 to 4μm.
 11. A battery case formed by subjecting a surface-treated steelplate for a battery case in accordance with claim 1 or 2 to adeep-drawing method, a DI-forming method or a DTR-forming method.